Patent Application
20080257180
This invention relates to an improved apparatus and method for dampening a printing press, and has particular but not exclusive application to a rotary offset printing press.
A web-offset rotary printing press comprises a number of printing units designed to print matter onto a continuous web of print medium, such as paper, travelling through each print unit. Each unit contains a cylinder group or print couple pair that comprises a rotatably mounted plate cylinder, to which one or more printing plates are attached, and a rotatably mounted blanket cylinder. Many presses of this type incorporate a shaftless drive system in which each cylinder group is driven by its own drive motor which directly drives one of the cylinders of the group via a belt or gear drive. The cylinders within each cylinder group are typically coupled mechanically so that drive is transferred from the directly driven cylinder to the other cylinders of that group.
An inking system is associated with each print couple, comprising a train of ink rollers operable to feed ink onto the printing plates as the plate cylinder rotates. The web of print medium passes between the blanket cylinder and an impression cylinder. The cylindrical surfaces of the plate and blanket cylinder are in rolling contact, so that an inked image is transferred onto the blanket cylinder from the plate cylinder and, from the blanket cylinder, to the print medium. To enable the paper web to be printed on both sides, the impression cylinder is actually the blanket cylinder of another print couple including a plate cylinder having printing plates to which ink is transferred from another inking system roller train. Thus, a pair of print couples is provided, with each couple on an opposite side of the paper web, which runs between them.
Each printing unit has a frame to which each print couple and its respective inking system are mounted. The printing unit also has a dampening system associated with each inking unit also mounted to the frame.
The printing units are spaced from each other and aligned with a folder unit so that the paper web is fed through each print unit from a separate reelstand mounted below or to one side of each printing unit at floor level and then travels in a lateral direction away from the unit and into the folder. A slitting mechanism is located between the print unit and the folder, for cutting the web into separate ribbons. Turner bars are provided for turning one or more of the ribbons to orientate them before they enter the folder.
In large scale high volume presses used for example in the printing of newspapers, multi-colour printing is achieved by providing each printing unit with a number of printing couple pairs mounted vertically one above the other in a stack so that the paper web travels in a vertically upward direction between each pair of print couples from the reelstand. A unit having four printing couple pairs, i.e. eight print couples, is able to print up to four colours on each side of the paper web and is often known as a “four-high” unit. A unit having a different number of print couple pairs is also possible depending on the application to which the press is to be put and the quality and number of colours to be printed. For example, a “five-high” unit having five print couple pairs is also known. When a printed web emerges from the upper end of each print unit it is passed over a roller having an axis of rotation at right angles to the direction of travel of the web. As the web passes over the roller its upward direction of travel is changed so that it now travels in a lateral direction along the press and towards the folder.
Considering the inking system in more detail, it includes a metering element to meter the ink film supplied through the ink roller train to the print cylinder. The inking system may comprise a fountain inker in which a fountain of ink washes over an inking roller and is then transferred through the inking system roller train to the plates on the plate cylinder. An alternative inking approach is used in the Goss Colorflow™ system in which helical brushes transfer ink from an ink source onto the roller for transfer through the roller train onto the plates on the plate cylinder. Also, digital inking techniques have been used widely hitherto. The flow of ink needs to be carefully controlled to obtain suitable distribution across the printing plates and the ink supply rate needs to be metered as a function of the operating speed of the press in order to ensure adequate print quality on the printed web.
The dampening system applies an aqueous dampening fluid onto the plates on the plate cylinder through a dampening roller train. The dampening fluid improves the quality of printing and facilitates transfer of the ink from the plates on the plate cylinder onto the web via the blanket cylinder. Hitherto, a spray bar system has been employed in which nozzles mounted along a common fluid supply conduit, spray the fluid onto individual zones of a roller in the dampening fluid roller train, so that the fluid is transferred through the train onto the plates on the plate cylinder. The flow rate through each of the nozzles is individually controllable and needs to be carefully adjusted to achieve optimum print quality for the printed web. If too much fluid is applied it may wash out the ink on the printed web. Also, excess fluid may work back through the inking system if a fountain system is used, so as to degrade the ink supply. If not enough fluid is applied, patchy printing may be produced on the web. Hitherto, the setting of the flow rate for the individual nozzles has been carried out empirically by the press operator by monitoring the quality of the printed web and making suitable adjustments. At the start of the print run, the nozzle settings are made on the operator's best judgement of suitable values. Thus a number of unwanted poor quality copies may occur at the start of a print run whilst the settings are adjusted, reducing the productivity of the press.
Another problem is that the nozzles may become impeded with dirt or even blocked and the performance of individual nozzles on the spray bar cannot be determined easily. Thus regular maintenance is required, which involves removal and cleaning of an entire spray bar.
The present invention seeks to overcome these problems.
According to the invention there is provided apparatus for dampening a printing press, comprising an outlet for dispensing a dampening fluid to the press, a flow rate setting device to set the flow rate of the dampening fluid to the press through the outlet, and a controller operable to control the setting device, the controller being operable to set an initial flow rate for the commencement of a print run to an initial setting value dependent on a stored value derived during at least one preceding print run, to receive updated data corresponding to an updated flow rate for the commenced print run, and to calculate said stored value in dependence upon said initial setting value and the updated data.
Thus, the dampening fluid setting for a print run is configured initially depending on the setting for one or more previous print runs, thereby providing a self learning system, with the advantage of greatly reducing the setting up time and the production of poor quality copies at the beginning of the print run
The updated data may derived by inspecting printed copy produced during the commenced print run and adjusting the setting device to optimise the printed copy, whereby the resulting setting of the setting device corresponds to the updated data. A manually operated input may be provided for adjusting the setting device so as to provide the updated data or the updating may be carried out automatically using a detector that senses the print quality.
A counter may be used to determine when a predetermined number of printed copies have been produced so that the printed copy can be inspected and the updated data obtained by adjusting the setting device.
The calculated value may be stored in a store together with a default setting value, and the controller may be operable to set the initial flow rate in dependence on the default setting value and the calculated stored value. Thus the self learning may be performed relative to a baseline set by the default value.
The controller can be configured to compute an offset value corresponding to the difference between the initial setting value and the updated data, and the calculated stored value is then calculated in dependence upon the offset value.
Individual instances of the offset value for a plurality of successive print runs, and the calculated stored value may be computed as an average of these offset values. The average may comprise a running average of a predetermined number of the offset values for the successive print runs.
An alarm detector may be provided to provide an alarm signal when the flow rate setting adopts a predetermined relationship to an alarm threshold level. This enables early identification of a degradation of performance of the outlet, for example due to a blockage.
The outlet may comprise a nozzle and the flow rate setting device may comprise an associated valve selectively operable to adjust said flow rate of dampening fluid through the nozzle in a range of settings. The valve may comprise a solenoid operated valve cyclically operable between open and closed positions, and the controller may vary the relative periods that the valve is open and closed so as to provide the range of flow rate settings.
A plurality of the outlets may be provided, for example on a spray bar, each for dispensing said dampening fluid, with individual setting devices, and the controller may operable to control the setting devices individually in a plurality of individually controllable dampening zones.
The invention also includes a method of dispensing a dampening fluid in a printing press, through an outlet having an associated a flow rate setting device, comprising setting the device to an initial setting value for the commencement of a print run, the an initial setting value being dependent on a stored value derived during at least one preceding print run, receiving updated data corresponding to an updated flow rate for the commenced print run, calculating said stored value in dependence upon said initial setting value and the updated data, and storing said calculated value for use in setting the initial setting value for a subsequent print run.
In order that the invention may be more fully understood an embodiment thereof will now be described by way of example with reference to the accompanying drawings in which:
Referring to
Each printing unit is operative to print a different coloured ink on to the web 2 and in the example of
Considering the unit 1a in more detail, it includes a cylinder group 3 that comprises a rotatably mounted plate cylinder 4, to which one or more printing plates are attached (not shown), and a rotatably mounted blanket cylinder 5. The cylinders of cylinder group 3 are mounted for rotation in a frame 6 shown in
An inking system 9 associated with the cylinder group 3 feeds ink onto the printing plates on a plate cylinder 4 as it rotates. The ink contained in the reservoir 10 is transferred onto a rubber inking roller 11 and then through the rollers 12-21 onto the surface of the plates on the plate cylinder 4. The arrangement of the reservoir 10 and inking roller 11 may comprise a fountain inker in which a fountain of ink washes over the inking roller 11. Alternatively, the arrangement 10, 11 may comprise a Goss Colourflow™ system in which a rotary helical brush transfers ink from the reservoir 10 onto the ink roller 11. Alternatively, digital inking techniques may be employed.
The print unit 1a also includes a dampening system 22 for applying a dampening fluid onto the plates on cylinder 4. The dampening system includes a dampening fluid roller train comprising rollers 23, 24, 25 and a spray bar 26 contained within a trough 27. As shown in
Each of the nozzles 29 sprays fluid onto the individual zone of the roller 23, so as to be transferred to a corresponding zone of the plate cylinder 4. The rollers 23, 25 may comprise rubber rollers and the roller 24 may comprise a roller with a chromed surface having hydrophilic properties to aid in transferring the dampening fluid along the roller train.
The nozzles 29 are provided with a solenoid operated valve to control the flow rate of dampening fluid onto roller 23. Each of the valves is controlled individually by a spray bar controller 30 which in turn is controlled by a workstation 31. A sectional view through one of the nozzles is shown in
Thus, in use, the printing plates on cylinder 4 are both inked and provided with dampening fluid so that, referring to
As shown in
It will be understood that the blanket cylinder 5′ acts as an impression cylinder for the blanket cylinder 5 and vice versa. The paper web 2 is fed from a reelstand (not shown) through the print units 1 successively and then to a splitter and folder (not shown) in a manner well known in the art. The arrangement shown in
As previously explained, the dampening fluid improves the quality of printing and the transfer of the ink from the plates on plate cylinder 4 onto the printed web 2. If too much fluid is applied, it may wash out the ink on the printing web 2. Also, excess fluid may work back through the inking system 9 so as to degrade the ink supply in the reservoir 10 if a fountain system is used. Conversely, if not enough dampening fluid is applied, patchy printing may be produced on the web.
In accordance with the invention, the settings for the flow rate of the nozzles 29-1: 29-8 is set under the control of a program 46 run by the workstation 31, utilising data held in a data store 47. It will be appreciated that in practice, the control program 46 and data store 47 will be within the conventional memory of the work station 31 and selected for operation by means of its keyboard 48 so as to be run by its internal microprocessor. Various operational parameters for the program are displayed on the screen 49 of the workstation 31.
The control program 46 controls operation of the spray bar controller 30 so as to set the flow rate for the nozzles 29-1: 29-8 individually on the basis of default settings stored in the data store 47 and also averaged, updated settings derived from successive print runs. The flow rate is controlled by varying the time that each solenoid operative valve 29 is switched on during a duty cycle. Thus, for example, if the solenoid operated valves 29 are switched on and off at a constant duty cycle of e.g. 5 Hz, this corresponds to a valve cycle time of 200 Ms. As shown in Table 1 below, a series of default settings D are illustrated for setting the on-times of the individual nozzles 29-1: 29-8. Thus, for nozzle 29-1, the default on-time D is 26 Ms, which means that the default open time for valve 29-1 is 26 Ms and that it will be closed for the remainder of the 200 Ms period. Corresponding individual default times D for the other nozzles 29-2: 29-8 are shown. These default settings D may be derived using the best skill and knowledge of the print process operator when the printing press is first set up for operation. In accordance with the invention, these default setting are modified by a parameter AVOFS, which is an average offset computed in dependence upon data derived from successive print runs, as will be explained in more detail later. Thus, for each print run, an initial setting IS for each nozzle 29 is determined, based on the default setting D and the value of the offset AVOFS from the default setting, as shown by way of example in Table 1.
At step s4.2, initial settings for the nozzle 29 (IS) are computed based on the sum of the default settings D and the correction AVOFS which are both held in the data store 47. For the first print run, each value of AVOFS is typically zero, but thereafter becomes updated by the process described below.
At step s4.3, the print run starts and at step s4.4, the print run parameter N is incremented.
The press is then allowed to run up to speed and reach its normal operating temperature e.g. by printing X=3,000 copies. The print number may be counted by a counter function performed by the workstation 31 on the basis of the usual data available to it from the press, which may be provided by sensors (not shown). This counting function is illustrated at step s4.5.
Then, at step s4.6, the operator visually inspects the quality of the printed copy on web 2 as illustrated at 49 in
Alternatively, a detector 50 may be employed to detect the print quality automatically and provide data to the workstation 31, as shown in
At step s4.7, an offset OFS is calculated for the print run based on the difference between the initial settings IS and the actual settings AS for the nozzles 29 individually.
The print run then is continued using the actual settings AS i.e. the settings which optimise print quality for the particular print run.
At steps s4.8 and s4.9A or s4.9B, an average of the offset OFS, namely AVOFS is computed for successive print runs and is thereafter used at step s4.10 to update the stored value held in data store 47. In general terms, the value of AVOFS is computed as a running average of the last P offset values OFS i.e. the offset values for the last P print runs. For example, the average may be taken over the last P=10 print runs.
For the first print run, N is less than P as determined at step s4.8 and so the average is computed at step s4.9A. In fact, for the first print run, the single computed value of OFS is used to update the value of AVOFS held in store 47, which was initially zero. For the next print run where N=2 and hence N<P, AVOFS is computed at step s4.9A to be the average OFS for the first two print runs and the value of AVOFS is updated in store 47 at step s4.10. The process continues until P=10 print runs have occurred and thereafter, the value of AVOFS is computed at step s4.9B so as to be a running average of OFS for the last P=10 print runs.
Each print run ends at step s4.11 and the next print run is initiated at step s4.12 when the initial settings IS for the individual nozzles 29 are set according to the values computed at step s4.2.
The described control routine has the advantage that the individual settings for the nozzles 29 can be maintained more accurately, based on the data from preceding print runs. Moreover, because an average is taken, spurious readings produced during one print run do not produce wild swings for the initial settings IS for the subsequent print run.
Thus, in accordance with the invention, the settings for the flow rate through the individual nozzles 29-1: 29-8 are set individually and are continuously updated on the basis of data from preceding print runs. This has the advantage that at start up of print run, the number of trial copies that need to be printed and discarded is materially reduced since the initial settings IS are more closely based on the likely actual settings AS needed for the run, rather than being based solely on the print press operators' best judgement.
Also the self learning system has the advantage that if a nozzle becomes partially blocked over time, the stored value of the average offset AVOFS adjusts the initial settings IS for the next print run so as to take account of and compensate for the partial blockage.
The invention also allows a predetermined threshold to be set for the flow rate through the nozzles individually so that if a nozzle becomes blocked so as to result in a spray flow rate below a predetermined threshold limit, an alarm signal can be produced to notify the machine operator that servicing is required for the particular nozzle 29. Referring to
The display on screen 49 may also include a display of the alarm limits, i.e. thresholds T1 and T2, a cursor operated control to allow the number X of copies to be adjusted before the actual values AS are set, and also a display of the actual values AS currently being used together with the corresponding value of AVOFS for each nozzle.
Also, the apparatus may be switchable between the previously described self learning mode and a mode in which the default values D alone are used as the settings, under the control of the press operator.
Furthermore, the screen may include a display which corresponds to the physical arrangement of print units 1 in a particular press, which is configurable for different print units depending on the architecture of a particular print press installation.
Many modifications and variations fall within the scope of the invention as set out in the claims. For example, whilst the flow rate of the spray nozzles 29 has been described as being controlled by the solenoids energised at a fixed frequency with a variable duty cycle, it will be understood that the frequency itself can be varied whilst using a fixed on-time, or both the duty cycle and the frequency can be varied. Other flow rate control schemes can be used and for example analogue control valves can dispense the dampening fluid, operated by an analogue control signal to control the fluid flow rate.
The invention is not restricted to newspaper printing presses and can be used in any press that utilises a dampening fluid system.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0417586.5 | Aug 2004 | GB | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2005/053647 | 7/26/2005 | WO | 00 | 11/26/2007 |
